From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Date: Wed, 13 Aug 2008 12:46:38 +0000
Subject: Re: Serial stdio overwhelming interrupts
Message-Id: <48A2D7AE.80109@linux.vnet.ibm.com>
List-Id: <kvm-ppc.vger.kernel.org>
References: <E20ABADA5792574791053954EC20B5952C59A4@zch01exm26.fsl.freescale.net>
In-Reply-To: <E20ABADA5792574791053954EC20B5952C59A4@zch01exm26.fsl.freescale.net>
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To: kvm-ppc@vger.kernel.org

Liu Yu wrote:
> Hi guys,
>
> In my kvm machine, I use serial as its default stdio.
> But when display a number of characters, e.g. cat a big ascii file,=20
> the serial always hangs as encount overwhelming interrupts, and then outp=
ut a kernel log "serial8250: too much work for irq 42".
>
> I found that the serial in qemu is primitive so that it generate a interr=
upt on every single character.=20
> This make it easier to reach the threshold of reporting "too much work".
>
> I had to use the patch below to get this issue walked arroud.
>
> Have you guys ever met the serial hanging problem before?
>  =20

We had that some times in the beginning while we brought up interrupts.
But since that time it did never occur again and I thought we fixed it.
Maybe your use case of catting a file to it is stressing it now to a new=20
extend triggering it again.

> ---
> diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
> index be95e55..af3e569 100644
> --- a/drivers/serial/8250.c
> +++ b/drivers/serial/8250.c
> @@ -70,7 +70,7 @@ static unsigned int nr_uarts =3D CONFIG_SERIAL_8250_RUN=
TIME_UARTS;
>  #define DEBUG_INTR(fmt...)	do { } while (0)
>  #endif
> =20
> -#define PASS_LIMIT	256
> +#define PASS_LIMIT	65535
> =20
>  /*
>   * We default to IRQ0 for the "no irq" hack.   Some
>
> Best Regards.
> =20
> Yu
> N=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BDr=EF=BF=BD=EF=BF=BDy=EF=BF=
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=BD)=DE=BA{.n=EF=BF=BD+=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BDjir)=EF=BF=BD=EF=
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=EF=BF=BD=EF=BF=BD2=EF=BF=BD=DE=99=EF=BF=BD=EF=BF=BD=EF=BF=BD&=EF=BF=BD)=DF=
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=BF=BD=D9=A5


--=20

Gr=C3=BCsse / regards,=20
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization